If I read this 2005 BBA document correctly, the '05 F250 and F350 SRW 4x4's ought to have a Dana 60 rated at 6000 lbs with 9.75" ring gear, the F350 DRW should have a Dana Super 60 rated also at 6000 lbs but with a 10.0" ring gear while the F450 and F550's have a Dana Super 60 rated at 7000 lbs with a 10.0" ring gear.
That is even more interesting... I wonder what else is different on these 'super 60's, axleshaft diameter? spline count? stub shafts? The Dana website doesn't offer any information on it. They list the 60 front with only a 4300 lb gross weight rating, the 70 front with only a 5700 lb rating and the 60 full-float rear with 6000 lb rating....
There are a few changes in axle choices and specs for 2005.
The 2005 Dana 60 and Super 60 have an axle shaft minimum diameter of 1.356", and 1.47" diameter over the splines with 35 splines. Again, the D60 for F250, F350SRW and F350DRW is rated at 6000lbs while the D S60 for the f450 and F550 is rated at 7000 lbs.
Compare that to the 2003 (2004 and before) Dana 60's with an axle shaft minimum diameter of 1.59", and 1.30" diameter over the splines with 30 splines. The D60 for the F250, F350 SRW and DRW was rated at 5200lbs while the D60 for the F450 and F550 was rated at 6000 lbs.
The rear axle ratings also took a pretty good hit. The choices are a little different too.
In 2003, we had 6 axle "choices" :
1) Visteon 10.5" rated at 6830lbs for the F250/F350 SRW
2) Visteon 10.5" dually rated at 8250lbs for F350 DRW pickup w/ 5.4L
3) Visteon 10.5" dually rated at 9750 lbs for F350 DRW Chassis Cab w/ 5.4L
4) Dana 80 rated at 11,000 lbs for the F350 DRW w/ 6.0L and 6.8L and F450's
5) Dana S110 rated at 13,500lbs for F550's.
6) Dana S110 rated at 14,500 lbs for F550's w/ 22,000lbs GVWR
Now, for 2005, there's 7 different axle rating choices:
1) Visteon 10.5" rated at 6200 lbs for F250's (what??? that can't be right!)
2) Visteon 10.5" rated at 7280 lbs for F350 SRW's (Que??? No cano be-o el correcto!)
3) Visteon Dually 10.5" rated at 9750lbs for F350 DRW w/5.4L Chassis Cab
4) Dana 80 rated at 9750 Lbs for F350 DRW Chassis Cab with 6.0L and 6.8L
5) Dana 80 rated at 9000 lbs for F350 DRW pickups (No shizzle for my duallizzle????)
6) Dana S110 rated at 12,000 lbs for F450's
7) Dana S110 rated at 13,660 lbs for F550's
The ring gear sizes, axle shaft minor and major diameter and spline count in 2003 were:
One correction, in 2003 (2004 and prior), the F550 had the Dana S135 axle not the S110, hence the apparent reduction in size from the massive 14.38" ring gear of the S135 to the more "reasonable" 11.8" ring gear of the 2005 S110.
I was thinking about that S-135 and S-110 axle thing. Dana gives some pretty in-depth specs on the Roadranger site about the S-110 series axles but very little on the S-135. Seems like the 110 series is the better axle choice to me, despite the ring gear size difference.
Visteon lists all the 10.5" axles, SRW and DRW, as 9750 lbs on their website and the same torque and GCWR specs as well. Sounds like the rating differences Ford applies to them are due more to differences in the rest of the rear suspension of the different models of trucks, probably mostly the springs, but the carrier info you stated is interesting too.
Dana rates the Dana80 in general at 11,000 or 11,500 lbs on thier website. Most of the different truck manufacturers using seem to rate it differently once it's in the truck though.
Thanks for taking the time to post up the details you found, it does help clear up some of the mysteries at least.
The way I understand it is that the shaft necks down a little near the splines to absorb twist. I have aftermarkets shafts for several axles and they all have a little smaller diameter near the spline. When the shaft neck down after the splines, the twisting force is handled in the smaller area like a torsion bar and keeps the shock loads away from the splines. This makes the shaft stronger. I think Ford is just following suit. The minimum diameter of 1.356 occurs only in this small area or section of the shaft. I have seen the shafts from the Super Duty Dana 60 and they are really impressive pieces.